Abstract:

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Recent observations relevant to the early stages of the fatigue damage of crystalline
materials are reviewed. Experimental evidence on the localization of the cyclic plastic strain and on
the surface relief formation in cyclic loading of 316L austenitic stainless steel is presented. The
focused ion beam is used for exposing three-dimensional evidence of persistent slip markings
(PSMs). PSMs consist of extrusions and parallel or alternating intrusions which develop during
cyclic loading. Monte Carlo simulations of vacancy generation within persistent slip band (PSB)
and their migration to the matrix where they annihilate on the edge dislocations are used to simulate
the growth of extrusions and intrusions. The results of the simulations are compared with
experimental data and discussed in terms vacancy models of fatigue crack initiation.

Abstract: Effects of extrusion on mechanical properties and damping capacity of Mg-1.8wt.%Cu
-0.5wt.%Mn (MCM1805) alloy have been investigated. Tensile tests and dynamic mechanical
analyzer were respectively used to measure tensile properties and damping capacity at room
temperature of as-cast and as-extruded MCM1805 alloy. The microstructure was studied using optical
microscope, X-ray diffraction and scanning electron microscope with an energy dispersive X-ray
spectrometer. Granato-Lücke model was used to explain the influences of extrusion on damping
capacity of MCM1805 alloy. The results showed that extrusion dramatically decreases the grain size
but has little influence on phase composition and solute atoms concentration of MCM1805 alloy, and
the grain refinement was the dominant reason for the obvious increase of tensile properties and
decrease of internal friction of MCM1805 alloy.

Abstract: Grain refinement and crystal orientation of magnesium alloy AZ31 under torsion extrusion with a square-hole die are investigated. The optimum temperature and ratio of the die rotation speed to the extrusion speed were clarified, resulting in uniformly distributed fine grains with sizes in the range 1- m over the entire cross section of the worked specimen. The crystal orientation of the specimen was determined by electron backscatter diffraction and compared with that of a conventionally extruded specimen. In the case of torsion extrusion, a very strong <0001> texture was observed along the extrusion axis, especially in the center region of the cross section. In contrast, the <0001> direction of many grains in the conventionally extruded specimen tended to be perpendicular to the extrusion axis.

Abstract: Equal channel angular extrusion (ECAE) is a severe plastic deformation (SPD) method for obtaining bulk nanostructured materials. The ECAE die consists of two equal channels that intersect at an angle, usually between 90° and 135°. In the present study, the plastic deformation behavior of the Cu during the ECAE process with 120° die through multiple passes was investigated. Finite element modelling was included in order to analyze the deformation behavior as the material passes through the die. In order to perform the FEM simulations the properties of the commercial purity Cu have been selected.

Abstract: Lotus-type porous aluminum with cylindrical pores oriented in one direction was deformed by Equal Channel Angular Extrusion (ECAE) through a 150° die with sequential 180° rotations, and the pore morphology and Vickers hardness after the extrusion were investigated. The Vickers hardness increases with increasing number of passes in the extrusions both parallel and perpendicular to the pore direction, accompanied by the decrease of porosity. The densification occurs more easily in the perpendicular extrusions than in the parallel extrusions, and the large deformation by the densification gives rise to the large increase in the Vickers hardness for the perpendicular extrusions.

Abstract: Severe plastic deformation is one of the emerging and promising techniques applied to bulk materials to produce fine grain structure with attractive properties. This study aims to investigate the effect of extrusion parameters like extrusion temperature, number of passes on the equal channel angular pressing and twist extrusion forming behavior of AA7075-T6 Aluminum alloy by hot extrusion process. AA7075-T6 samples of 70x28x18 mm cross sections extruded by equal channel angular pressing and twist extrusion process was subjected to microstructure analysis, hardness and tensile tests in order to determine their mechanical properties. As a result of the experiments, it was determined that twist extrusion leads to more grain refinement at high temperatures with more number of passes compared to equal channel angular pressing. SEM micrographs show that there is severe orientation of the grains facilitated by the extrusion process which enhances the strength. The dense banding of the grains had effected in marginal hardness enhancement in the matrix of the specimens processed by twist extrusion and equal channel angular extrusion process.